This invention relates to an air bleed type carburetor for supplying an air-fuel mixture to an engine mounted on a vehicle, especially to an air bleed type carburetor which can vary the operating characteristics of a carburetor for obtaining a desirable enriched air fuel ratio in accordance with changes in altitude and with changes in the operating characteristics of the engine.
In conventional carburetors, the air fuel ratio is enriched for obtaining increased engine power when the throttle valve of the carburetor is opened. On the other hand, since the conventional carburetors, especially fixed venturi carburetors, mix a certain volume of air with a certain volume of fuel, when a vehicle which has the conventional carburetor mounted thereon is at high altitude, due to the decrease of the atmospheric pressure (and the specific weight of air), the total amount of intake air in weight is decreased and air fuel ratio is enriched. As a result, harmful contaminants, such as carbon monoxide (CO) and hydro carbon (HC) contained in exhaust gas emitted from the engine are increased and an engine power drop is caused. In addition, since the throttle valve is frequently opened due to the engine power drop at high altitude, the harmful CO and HC contaminants contained in the exhaust gas emitted from the engine can be further increased.
In the copending application Ser. No. 845,601 filed on Oct. 26, 1977, the applicant of the present invention has provided an altitude compensating system of a carburetor for obtaining a desirable enriched air fuel ratio, so as to obviate the above-mentioned problems. The system comprises: a device for enriching the air fuel ratio after the engine load has reached a predetermined first value; an altitude compensating valve device for supplying compensating air in accordance with changes in altitude; a control valve device communicated with the altitude compensating valve device for permitting the compensating air to pass after the engine load has reached a predetermined second value, and; a switching valve device disposed at a position between the control valve device and a main jet of a carburetor and interlocked with a throttle valve of the carburetor for switching the compensating air.